The present invention generally relates to thermal transfer printing, and particularly, to a thermal transfer medium and a method of making thereof.
Thermal transfer printing is widely used in special applications such as in the printing of machine-readable bar codes on labels or directly on articles to be coded. The thermal transfer process employed by these printing methods provides great flexibility in generating images and allowing for broad variations in style, size and color of the printed images, typically from a single machine with a single thermal print head. Representative documentation in the area of thermal transfer printing includes the following patents:
U.S. Pat. No. 3,663,278, issued to J. H. Blose et al. on May 16, 1972, discloses a thermal transfer medium having a coating composition of cellulosic polymer, thermoplastic resin, plasticizer and a xe2x80x9csensiblexe2x80x9d material such as a dye or pigment.
U.S. Pat. No. 4,315,643, issued to Y. Tokunaga et al. on Feb. 16, 1982, discloses a thermal transfer element comprising a foundation, a color developing layer and a hot melt ink layer. The ink layer includes heat conductive material and a solid wax as a binder material.
U.S. Pat. No. 4,403,224, issued to R. C. Winowski on Sep. 6, 1983, discloses a surface recording layer comprising a resin binder, a pigment dispersed in the binder, and a smudge inhibitor incorporated into and dispersed throughout the surface recording layer, or applied to the surface recording layer as a separate coating.
U.S. Pat. No. 4,463,034, issued to Y. Tokunaga, et al. on Jul. 31, 1984, discloses a heat-sensitive magnetic transfer element having a hot melt or a solvent coating.
U.S. Pat. No. 4,523,207, issued to M. W. Lewis et al. on Jun. 11, 1985, discloses a multiple copy thermal record sheet which uses crystal violet lactone and a phenolic resin.
U.S. Pat. No. 4,628,000, issued to S. G. Talvalkar et al. on Dec. 9, 1986, discloses a thermal transfer formulation that includes an adhesive-plasticizer or a sucrose benzoate transfer agent and a coloring material or pigment.
U.S. Pat. No. 4,687,701, issued to K. Knirsch et al. on Aug. 18, 1987, discloses a heat sensitive inked element using a blend of thermoplastic resins and waxes.
U.S. Pat. No. 4,698,268, issued to S. Ueyama on Oct. 6, 1987, discloses a heat resistant substrate and a heat-sensitive transferring ink layer. An overcoat layer may be formed on the ink layer.
U.S. Pat. No. 4,707,395, issued to S. Ueyama, et al., on Nov. 17, 1987, discloses a substrate, a heat-sensitive releasing layer, a coloring agent layer, and a heat-sensitive cohesive layer.
U.S. Pat. No. 4,777,079, issued to M. Nagamoto et al. on Oct. 11, 1988, discloses an image transfer type thermosensitive recording medium using thermosoftening resins and a coloring agent.
U.S. Pat. No. 4,778,729, issued to A. Mitsubishi on Oct. 18, 1988, discloses a heat transfer sheet comprising a hot melt ink layer on one surface of a film and a filling layer laminated on the ink layer.
U.S. Pat. No. 4,869,941, issued to Ohki on Sep. 26, 1989, discloses an imaged substrate with a protective layer laminated on the imaged surface.
U.S. Pat. No. 4,923,749, issued to Talvalkar on May 8, 1990, discloses a thermal transfer ribbon which comprises two layers, a thermal sensitive layer and a protective layer, both of which are water based.
U.S. Pat. No. 4,975,332, issued to Shini et al. on Dec. 4, 1990, discloses a recording medium for transfer printing comprising a base film, an adhesiveness improving layer, an electrically resistant layer and a heat sensitive transfer ink layer.
U.S. Pat. No. 4,983,446, issued to Taniguchi et al. on Jan. 8, 1991, describes a thermal image transfer recording medium which comprises as a main component, a saturated linear polyester resin.
U.S. Pat. No. 4,988,563, issued to Wehr on Jan. 29, 1991, discloses a thermal transfer ribbon having a thermal sensitive coating and a protective coating. The protective coating is a wax-copolymer mixture which reduces ribbon offset.
U.S. Pat. Nos. 5,128,308 and 5,248,652, issued to Talvalkar, each disclose a thermal transfer ribbon having a reactive dye which generates color when exposed to heat from a thermal transfer printer.
And, U.S. Pat. No. 5,240,781, issued to Obatta et al., discloses an ink ribbon for thermal transfer printers having a thermal transfer layer comprising a wax-like substance as a main component and a thermoplastic adhesive layer having a film forming property.
Generally, thermal transfer ribbons are made by applying the release and functional layers to a substrate in successive stages until the ribbon is substantially complete because the release layer and back coat are generally not stable when in contact with one another.
This is particularly a disadvantage when ribbons are to be completed by the deposition of the functional layer at a site remote, such as a printing station in a warehouse, from the facility used to prepare the laminate. Applying the functional coat remotely can provide flexibility in choosing various functional coats to be applied to the labels depending on the circumstances. In such situations, it is desirable to minimize the number of different layers that must be applied to the substrate to complete a ribbon to reduce the complexity, time, and costs for manufacturing the ribbons.
Consequently, it would be desirable to provide a laminate which need only be coated with the functional coating to complete the ribbon.
It is a feature of the present invention to provide a thermal transfer medium, such as a thermal transfer ribbon, having a substrate with a coating incorporated thereon. The coating aids the release of a subsequently applied functional layer.
The present invention relates to a thermal transfer medium which transfers images to a receiving substrate or an article. The thermal transfer medium comprises a laminate, having a substrate and a coating positioned on at least one surface thereof. The coating has protrusions with a length/width ratio of not less than about 3 and at a density of not less than about 20 protrusions/100 micrometer squared, and a functional layer positioned substantially on the coating.
The present invention also relates to another class of thermal transfer media which transfer images to a receiving substrate. These thermal transfer media comprise a laminate, having a substrate and a coating comprising a silicone resin and/or an oil/wax positioned substantially on at least one surface of the substrate, and a functional layer positioned substantially on the coating. Thermal transfer media which fall into both classes are also included in this invention.
The present invention further relates to a method of thermally printing an article. The method may include providing a thermal printer having a roller and a thermal printhead, positioning an article proximate to the roller; and positioning a thermal transfer medium between the roller and the printhead.
Additionally, the present invention relates to a thermal transfer medium including a laminate having a substrate and coatings of silicone resin or an oil/wax composition on both sides. At least one coating can have protrusions with a length/width ratio of not less than about 3 and at a density of not less than about 20 protrusions/100 micrometer squared. A thermal transfer medium may be obtained by positioning a functional coat on one of the coatings, which upon heat exposure from the thermal printhead head, at least a portion of the functional coat transfers to the article.
Moreover, the present invention relates to a thermal transfer medium which transfers images to a receiving substrate. The thermal transfer medium includes a laminate. The laminate may further include a substrate, a first coating positioned substantially on one surface of the substrate having protrusions with a length/width ratio of not less than about 3 and at a density of not less than about 20 protrusions/100 micrometer squared, and a second coating positioned substantially on an opposing surface of the substrate from the first coating, wherein the second coating has protrusions with a length/width ratio of not less than about 3 and at a density of not less than about 20 protrusions/100 micrometer squared. Desirably, the compositions of the first and the second coatings are substantially the same.
In addition, the present invention relates to a method for preparing a thermal transfer medium. The method can include providing a substrate having a first side and a second side; coating the first and second sides of the substrate with a composition including a wax, an oil, a silicon polymer, or combination thereof to form a first coating and a second coating; and applying a functional coat to either the first or second coating.